What are some animals that eat meat and plants? | Reference.com What are some animals that eat meat and plants? A: Quick Answer Animals that eat meat and plants are called omnivores, of which humans are a prime example. Some other animals that are omnivores are bears, skunks, squirrels and red foxes. Full Answer Some reptiles, fish and insects also feed on plants and animals. For instance, the opaleye fish eat both seaweed and the small organisms that live in the seaweed. Box turtles feed on flowers and berries as well as fish and frogs. Ants are opportunistic eaters, feeding on nectar and seeds when possible and other insects if the opportunity arises. Racoons, another example of an omnivore, display characteristics of both carnivores and herbivores. They have sharp teeth for ripping flesh and flat molars for grinding up plants. Omnivores are readily adaptable animals, allowing them to live in extreme conditions. If meat is not available, omnivores can live on plants and vice versa. This is because omnivores can digest both protein and fiber, while carnivores receive no nutritional value from plant material.

Omnivores, along with carnivores, are part of the third trophic level. The first trophic level, which includes most plants, are called autotrophs because they produce their own food. The second trophic level includes herbivores, which eat autotrophs. Species in the third trophic level rely on organisms in the second trophic level for food completely or partially. Herbivores, Omnivores, and Carnivores About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students. Herbivores, Omnivores, and Carnivores Animals can be carnivores, herbivores, or omnivores in their eating strategies. Learning Objective Differentiate among herbivores, omnivores, and carnivores Key Points Herbivores are those animals, such as deer and koalas, that only eat plant material.

Omnivores are those animals, such as bears and humans, that can eat a variety of food sources , but tend to prefer one type to another. While most carnivores , such as cats, eat only meat, facultative carnivores, such as dogs, behave more like omnivores as they can eat plant matter along with meat. Facultative carnivores can eat meat as well as plant material while obligate carnivores eat meat all the time. Terms Full Text Herbivores, Omnivores, and Carnivores Herbivores are animals whose primary food source is plant-based. Examples of herbivores include vertebrates like deer, koalas, and some bird species , as well as invertebrates such as crickets and caterpillars . These animals have evolved digestive systems capable of digesting large amounts of plant material. The plants are high in fiber and starch, which provide the main energy source in their diet. Since some parts of plant materials, such as cellulose , are hard to digest, the digestive tract of herbivores is adapted so that food may be digested properly. Many large herbivores have symbiotic bacteria within their guts to assist with the breakdown of cellulose.

They have long and complex digestive tracts to allow enough space and time for microbial fermentation to occur. Herbivores can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters). Herbivores, such as this (a) mule deer and (b) monarch caterpillar, eat primarily plant material. Some herbivores contain symbiotic bacteria within their intestines to aid with the digestion of the cellulose found in plant cell walls. Omnivores are animals that eat both plant- and animal- derived food. Although the Latin term omnivore literally means "eater of everything", omnivores cannot really eat everything that other animals eat. They can only eat things that are moderately easy to acquire while being moderately nutritious. For example, most omnivores cannot live by grazing, nor are they able to eat some hard-shelled animals or successfully hunt large or fast prey. Humans, bears, and chickens are examples of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish .

Omnivores such as the (a) bear and (b) crayfish eat both plant- and animal-based food. While their food options are greater than those of herbivores or carnivores, they are still limited by what they can find to eat, or what they can catch. Carnivores are animals that eat other animals. The word carnivore is derived from Latin and means "meat eater." Wild cats, such as lions and tigers, are examples of vertebrate carnivores, as are snakes and sharks, while invertebrate carnivores include sea stars, spiders, and ladybugs . Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family. Facultative carnivores are those that also eat non-animal food in addition to animal food. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores. What is the term for animals that eat both plants and animals? | Reference.com What is the term for animals that eat both plants and animals? A: Quick Answer Omnivore is the term for animals that eat both plants and animals.

Human beings are prime examples of omnivores. Other examples include chickens, raccoons and flies. Full Answer The word "omnivore" is derived from Latin, and it means "all-eater." Scientists classify two general types of omnivores. First, there are omnivores that hunt for their food as well as forage for fresh plant matter. Second, there are omnivores that are classified as scavengers. These omnivores feed on already dead animals and plants. Some herbivores incidentally eat small amounts of animal food if that type of animal matter becomes available. Incidental consumption does not classify a living creature as an omnivore. Dental and Skull Anatomy of Carnivores, Herbivores, and Omnivores Fun Stuff Dental and Skull Anatomy of Carnivores, Herbivores, and Omnivores An animal’s diet is one of the most important aspects of its biology, and it helps shape the behavior, evolution, and anatomy of the species. The development and arrangement of an animal’s teeth, known as its dentition, reflects this best; but an animal’s skull evolves to suit its diet as well.

In general, meat-eating carnivores have teeth for tearing and skulls capable of biting with great force, while the plant-eating herbivores have teeth and skulls equipped to grind tough vegetation. Omnivores, which eat both plants and animals, have skulls and dentition suitable for a wide range of foods. These trends are so strong that paleontologists can often determine the diet of an extinct animal from nothing more than a few teeth or skull fragments. Carnivores Carnivorous animals subsist on the flesh, bones, and viscera of other creatures. Most carnivores have long, sharp teeth adapted to ripping, tearing or cutting flesh. While many also possess a few molars in the back of their mouths, and sharp incisors in the front, the most important teeth for carnivores are their long, sharp canine teeth. Carnivores drive these teeth through the flesh of their prey with the help of very large temporalis muscles, which are responsible for pulling the lower jaw upwards and backwards towards the skull. The temporalis muscles attach to the jaw at one end, and the top of the skull at the other end.

To help accommodate larger temporalis muscles, some predators have evolved to have an enlarged ridge, termed the sagittal crest that acts as an attachment point or anchor for the muscle. However, the sagittal crest is not exclusively limited to carnivores, as it also appears in many herbivorous primates as well. Additionally, because predators must capture and kill their food before they can eat it, some possess teeth that aid in prey capture. Cats, for example, use their four, long canine teeth to sever their prey’s spinal cord. Some snakes have even more specialized prey-capturing teeth that have evolved into hypodermic-needlelike fangs to deliver venom into their prey. Herbivores Herbivores survive by consuming plant material. While some are indiscriminate grazers that consume a variety of plants, others are specialists that only eat a single plant species. For example, goats may eat virtually any vegetation they encounter, but koalas subsist entirely on eucalyptus plants. In general, plant foods are difficult to breakdown and digest; so, many herbivores have several pairs of broad molars that they use to grind leaves, shoots, and twigs.

Often, herbivores feature ridged molars and jaws capable of moving sideways. Both of these traits help herbivores to grind their food more effectively. Most herbivores are missing canines entirely, and those that do possess them usually have very small or reduced canines that are not very important for chewing food. Some herbivores have large incisors for clipping or tearing vegetation, but they may only occur on the lower jaw. For example, most deer lack upper incisors and press their lower incisors against their hard, upper palate to rip twigs and branches from trees. By contrast, horses have both upper and lower incisors that they use to clip vegetation cleanly. Some herbivores have evolved teeth that are no longer involved in feeding at all. For example, the large tusks of elephants are highly modified incisors. Elephants use their tusks to manipulate items in their environment, dig for water, and defend themselves. Walruses and some pigs also feature incisors that have evolved into tusks used for foraging, defense, and intra-species combat. Omnivores Omnivores, such as raccoons, opossums, bears, and humans, are animals that consume both plant and animal material.

Accordingly, omnivores have dentition, skulls, and teeth suitable for handling a variety of foods. Most omnivores have evolved different types of teeth, located in different parts of their mouths. In such scenarios, each type of tooth excels at handling a different type of food. For example, humans use their incisors and canines for ripping and cutting, and their molars and premolars for grinding. Biologists describe animals with such teeth as having heterodont dentition. By contrast, the teeth of homodont animals, such as iguanas, are all the same shape. As with some carnivores that have teeth to aid in prey capture, some omnivores have teeth that help them to obtain, rather than process, their food. Rodents are famous for their long, continuously growing incisors, which they use to chew through husks, shells and wood. This allows them to access well-protected or difficult-to-access foods, such as nuts. Although rodents are omnivores that occasionally eat insects and scavenge carcasses, plant material makes up the bulk of their diet. Their dentition reflects this as well: Rodents have strong molars, yet lack canine teeth entirely.

Instead, rodents have a gap between their incisors and molars, termed a diastema. References Anatomy and Physiology of Animals/The Gut and Digestion - Wikibooks, open books for an open world Anatomy and Physiology of Animals/The Gut and Digestion From Wikibooks, open books for an open world original image by vnysia cc by Contents After completing this section, you should know: what is meant by the terms: ingestion, digestion, absorption, assimilation, egestion, peristalsis and chyme the characteristics, advantages and disadvantages of a herbivorous, carnivorous and omnivorous diet the 4 main functions of the gut the parts of the gut in the order in which the food passes down it The Gut And Digestion[ edit ] Plant cells are made of organic molecules using energy from the sun. This process is called photosynthesis. Animals rely on these ready-made organic molecules to supply them with their food. Some animals (herbivores) eat plants; some (carnivores) eat the herbivores. Herbivores[ edit ] Herbivores eat plant material.

While no animal produces the digestive enzymes to break down the large cellulose molecules in the plant cell walls, micro-organisms' like bacteria, on the other hand, can break them down. Therefore herbivores employ micro-organisms to do the job for them. There are three types of herbivore: The first, ruminants like cattle, sheep and goats, house these bacteria in a special compartment in the enlarged stomach called the rumen. The second group has an enlarged large intestine and caecum, called a functional caecum, occupied by cellulose digesting micro-organisms. These non-ruminant herbivores include the horse, rabbit and rat. Humans also have a cecum and can be classified as the third type of herbivorous class, along with orangutans and gorillas. Plants are a primary pure and good source of nutrients, however they are digested very easily and therefore herbivores have to eat large quantities of food to obtain all they require. Herbivores like cows, horses and rabbits typically spend much of their day feeding. To give the micro-organisms access to the cellulose molecules, the plant cell walls need to be broken down.

This is why herbivores have teeth that are adapted to crush and grind. Their guts also tend to be lengthy and the food takes a long time to pass through it. Eating plants have other advantages. Plants are immobile so herbivores normally have to spend little energy collecting them. This contrasts with another main group of animals - the carnivores that often have to chase their prey. Carnivores[ edit ] Carnivorous animals like those in the cat and dog families, polar bears, seals, crocodiles and birds of prey catch and eat other animals. They often have to use large amounts of energy finding, stalking, catching and killing their prey. However, they are rewarded by the fact that meat provides a very concentrated source of nutrients. Carnivores in the wild therefore tend to eat distinct meals often with long and irregular intervals between them. Time after feeding is spent digesting and absorbing the food. The guts of carnivores are usually shorter and less complex than those of herbivores because meat is easier to digest than plant material. Carnivores usually have teeth that are specialised for dealing with flesh, gristle and bone. They have sleek bodies, strong, sharp claws and keen senses of smell, hearing and sight.

They are also often cunning, alert and have an aggressive nature. Omnivores[ edit ] Many animals feed on both animal and vegetable material – they are omnivorous. Most primates are herbivorous but a few, such as chimpanzees and humans, belong to this category as do pigs and rats. Their food is diverse, ranging from plant material to animals they have either killed themselves or scavenged from other carnivores. Omnivores lack the specialised teeth and guts of carnivores and herbivores but are often highly intelligent and adaptable reflecting their varied diet. Treatment Of Food[ edit ] Whether an animal eats plants or flesh, the carbohydrates, fats and proteins in the food it eats are generally giant molecules (see chapter 1). These need to be split up into smaller ones before they can pass into the blood and enter the cells to be used for energy or to make new cell constituents. For example: The Gut[ edit ] The digestive tract, alimentary canal or gut is a hollow tube stretching from the mouth to the anus. It is the organ system concerned with the treatment of foods. At the mouth the large food molecules are taken into the gut - this is called ingestion.

They must then be broken down into smaller ones by digestive enzymes - digestion, before they can be taken from the gut into the blood stream - absorption. The cells of the body can then use these small molecules - assimilation. The indigestible waste products are eliminated from the body by the act of egestion (see diagram 11.1). Diagram 11.1 - From ingestion to egestion The 4 major functions of the gut are: 1. Transporting the food; 2. Processing the food physically by breaking it up (chewing), mixing, adding fluid etc. 3. Processing the food chemically by adding digestive enzymes to split large food molecules into smaller ones. 4. Absorbing these small molecules into the blood stream so the body can use them. The regions of a typical mammals gut (for example a cat or dog) are shown in diagram 11.2. Diagram 11.2 - A typical mammalian gut The food that enters the mouth passes to the oesophagus, then to the stomach, small intestine, cecum, large intestine, rectum and finally undigested material exits at the anus.

The liver and pancreas produce secretions that aid digestion and the gall bladder stores bile. Herbivores have an appendix which they use for the digestion of cellulose. Carnivores have an appendix but is not of any function anymore due to the fact that their diet is not based on cellulose anymore. Mouth[ edit ] The mouth takes food into the body. The lips hold the food inside the mouth during chewing and allow the baby animal to suck on its mother’s teat. In elephants the lips (and nose) have developed into the trunk which is the main food collecting tool. Some mammals, e.g. hamsters, have stretchy cheek pouches that they use to carry food or material to make their nests. The sight or smell of food and its presence in the mouth stimulates the salivary glands to secrete saliva. There are four pairs of these glands in cats and dogs (see diagram 11.3). The fluid they produce moistens and softens the food making it easier to swallow. It also contains the enzyme, salivary amylase, which starts the digestion of starch. The tongue moves food around the mouth and rolls it into a ball for swallowing.

Taste buds are located on the tongue and in dogs and cats it is covered with spiny projections used for grooming and lapping. The cow’s tongue is prehensile and wraps around grass to graze it. Swallowing is a complex reflex involving 25 different muscles. It pushes food into the oesophagus and at the same time a small flap of tissue called the epiglottis closes off the windpipe so food doesn’t go ‘down the wrong way’ and choke the animal (see diagram 11.4). Diagram 11.3 - Salivary glands Teeth[ edit ] Teeth seize, tear and grind food. They are inserted into sockets in the bone and consist of a crown above the gum and root below. The crown is covered with a layer of enamel, the hardest substance in the body. Below this is the dentine, a softer but tough and shock resistant material. At the centre of the tooth is a space filled with pulp which contains blood vessels and nerves. The tooth is cemented into the socket and in most teeth the tip of the root is quite narrow with a small opening for the blood vessels and nerves (see diagram 11.5).

In teeth that grow continuously, like the incisors of rodents, the opening remains large and these teeth are called open rooted teeth. Mammals have 2 distinct sets of teeth. The first the milk teeth are replaced by the permanent teeth. Diagram 11.5 - Structure of a tooth Types Of Teeth[ edit ] All the teeth of fish and reptiles are similar but mammals usually have four different types of teeth. The incisors are the chisel-shaped ‘biting off’ teeth at the front of the mouth. In rodents and rabbits the incisors never stop growing (open-rooted teeth). They must be worn or ground down continuously by gnawing. They have hard enamel on one surface only so they wear unevenly and maintain their sharp cutting edge. The largest incisors in the animal kingdom are found in elephants, for tusks are actually giant incisors. Sloths have no incisors at all, and sheep have no incisors in the upper jaw (see diagram 11.6). Instead there is a horny pad against which the bottom incisors cut. The canines or ‘wolf-teeth’ are long, cone-shaped teeth situated just behind the incisors.

They are particularly well developed in the dog and cat families where they are used to hold, stab and kill the prey (see diagram 11.7). The tusks of boars and walruses are large canines while rodents and herbivores like sheep have no (or reduced) canines. In these animals the space where the canines would normally be is called the diastema. In rodents like the rat and beaver it allows the debris from gnawing to be expelled easily. The cheek teeth or premolars and molars crush and grind the food. They are particularly well developed in herbivores where they have complex ridges that form broad grinding surfaces (see diagram 11.6). These are created from alternating bands of hard enamel and softer dentine that wear at different rates. In carnivores the premolars and molars slice against each other like scissors and are called carnassial teeth see diagram 11.7). They are used for shearing flesh and bone. Dental Formula[ edit ] The numbers of the different kinds of teeth can be expressed in a dental formula. This gives the numbers of incisors, canines, premolars and molars in one half of the mouth.

The numbers of these four types of teeth in the left or right half of the upper jaw are written above a horizontal line and the four types of teeth in the right or left half of the lower jaw are written below it. Thus the dental formula for the sheep is: 0.0.3.3 3.1.3.3 It indicates that in the upper right (or left) half of the jaw there are no incisors or canines (i.e. there is a diastema), three premolars and three molars. In the lower right (or left) half of the jaw are three incisors, one canine, three premolars and three molars (see diagram 11.6). Diagram 11.6 - A sheep’s skull The dental formula for a dog is: 3.1.4.2 3.1.4.3 The formula indicates that in the right (or left) half of the upper jaw there are three incisors, one canine, four premolars and two molars. In the right (or left) half of the lower jaw there are three incisors, one canine, four premolars and three molars (see diagram 11.7).

Diagram 11.7 - A dog’s skull Oesophagus[ edit ] The oesophagus transports food to the stomach. Food is moved along the oesophagus, as it is along the small and large intestines, by contraction of the smooth muscles in the walls that push the food along rather like toothpaste along a tube. This movement is called peristalsis (see diagram 11.8). Diagram 11.8 - Peristalsis Stomach[ edit ] The stomach stores and mixes the food. Glands in the wall secrete gastric juice that contains enzymes to digest protein and fats as well as hydrochloric acid to make the contents very acidic. The walls of the stomach are very muscular and churn and mix the food with the gastric juice to form a watery mixture called chyme (pronounced kime). Rings of muscle called sphincters at the entrance and exit to the stomach control the movement of food into and out of it (see diagram 11.9). Diagram 11.9 - The stomach Small Intestine[ edit ] Most of the breakdown of the large food molecules and absorption of the smaller molecules take place in the long and narrow small intestine.

The total length varies but it is about 6.5 metres in humans, 21 metres in the horse, 40 metres in the ox and over 150 metres in the blue whale. It is divided into 3 sections: the duodenum (after the stomach), jejunum and ileum. The duodenum receives 3 different secretions: 1) Bile from the liver; 2) Pancreatic juice from the pancreas and 3) Intestinal juice from glands in the intestinal wall. These complete the digestion of starch, fats and protein. The products of digestion are absorbed into the blood and lymphatic system through the wall of the intestine, which is lined with tiny finger-like projections called villi that increase the surface area for more efficient absorption (see diagram 11.10). Diagram 11.10 - The wall of the small intestine showing villi The Rumen[ edit ] In ruminant herbivores like cows, sheep and antelopes the stomach is highly modified to act as a “fermentation vat”. It is divided into four parts. The largest part is called the rumen.

In the cow it occupies the entire left half of the abdominal cavity and can hold up to 270 litres. The reticulum is much smaller and has a honeycomb of raised folds on its inner surface. In the camel the reticulum is further modified to store water. The next part is called the omasum with a folded inner surface. Camels have no omasum. The final compartment is called the abomasum. This is the ‘true’ stomach where muscular walls churn the food and gastric juice is secreted (see diagram 11.11). Diagram 11.11 - The rumen Ruminants swallow the grass they graze almost without chewing and it passes down the oesophagus to the rumen and reticulum. Here liquid is added and the muscular walls churn the food. These chambers provide the main fermentation vat of the ruminant stomach. Here bacteria and single-celled animals start to act on the cellulose plant cell walls. These organisms break down the cellulose to smaller molecules that are absorbed to provide the cow or sheep with energy. In the process, the gases methane and carbon dioxide are produced. These cause the “burps” you may hear cows and sheep making.

Not only do the micro-organisms break down the cellulose but they also produce the vitamins E, B and K for use by the animal. Their digested bodies provide the ruminant with the majority of its protein requirements. In the wild grazing is a dangerous activity as it exposes the herbivore to predators. They crop the grass as quickly as possible and then when the animal is in a safer place the food in the rumen can be regurgitated to be chewed at the animal’s leisure. This is ‘chewing the cud’ or rumination. The finely ground food may be returned to the rumen for further work by the microorganisms or, if the particles are small enough, it will pass down a special groove in the wall of the oesophagus straight into the omasum. Here the contents are kneaded and water is absorbed before they pass to the abomasum. The abomasum acts as a “proper” stomach and gastric juice is secreted to digest the protein. Large Intestine[ edit ] The large intestine consists of the caecum, colon and rectum.

The chyme from the small intestine that enters the colon consists mainly of water and undigested material such as cellulose (fibre or roughage). In omnivores like the pig and humans the main function of the colon is absorption of water to give solid faeces. Bacteria in this part of the gut produce vitamins B and K. The caecum, which forms a dead-end pouch where the small intestine joins the large intestine, is small in pigs and humans and helps water absorption. However, in rabbits, rodents and horses, the caecum is very large and called the functional caecum. It is here that cellulose is digested by micro-organisms. The appendix, a narrow dead end tube at the end of the caecum, is particularly large in primates but seems to have no digestive function. Functional Caecum[ edit ] The caecum in the rabbit, rat and guinea pig is greatly enlarged to provide a “fermentation vat” for micro-organisms to break down the cellulose plant cell walls. This is called a functional caecum (see diagram 11.12). In the horse both the caecum and the colon are enlarged.

As in the rumen, the large cellulose molecules are broken down to smaller molecules that can be absorbed. However, the position of the functional caecum after the main areas of digestion and absorption, means it is potentially less effective than the rumen. This means that the small molecules that are produced there can not be absorbed by the gut but pass out in the faeces. The rabbit and rodents (and foals) solve this problem by eating their own faeces so that they pass through the gut a second time and the products of cellulose digestion can be absorbed in the small intestine. Rabbits produce two kinds of faeces. Softer night-time faeces are eaten directly from the anus and the harder pellets you are probably familiar with, that have passed through the gut twice. Diagram 11.12 - The gut of a rabbit The Gut Of Birds[ edit ] Birds’ guts have important differences from mammals’ guts. Most obviously, birds have a beak instead of teeth. Beaks are much lighter than teeth and are an adaptation for flight. Imagine a bird trying to take off and fly with a whole set of teeth in its head!

At the base of the oesophagus birds have a bag-like structure called a crop. In many birds the crop stores food before it enters the stomach, while in pigeons and doves glands in the crop secretes a special fluid called crop-milk which parent birds regurgitate to feed their young. The stomach is also modified and consists of two compartments. The first is the true stomach with muscular walls and enzyme secreting glands. The second compartment is the gizzard. In seed eating birds this has very muscular walls and contains pebbles swallowed by the bird to help grind the food. This is the reason why you must always supply a caged bird with grit. In birds of prey like the falcon the walls of the gizzard are much thinner and expand to accommodate large meals (see diagram 11.13). Diagram 11.13 - The stomach and small intestine of a hen Digestion[ edit ] During digestion the large food molecules are broken down into smaller molecules by enzymes. The three most important groups of enzymes secreted into the gut are: Amylases that split carbohydrates like starch and glycogen into monosaccharides like glucose. Proteases that split proteins into amino acids.

Lipases that split lipids or fats into fatty acids and glycerol. Glands produce various secretions which mix with the food as it passes along the gut. These secretions include: Saliva secreted into the mouth from several pairs of salivary glands (see diagram 11.3). Saliva consists mainly of water but contains salts, mucous and salivary amylase. The function of saliva is to lubricate food as it is chewed and swallowed and salivary amylase begins the digestion of starch. Gastric juice secreted into the stomach from glands in its walls. Gastric juice contains pepsin that breaks down protein and hydrochloric acid to produce the acidic conditions under which this enzyme works best. In baby animals rennin to digest milk is also produced in the stomach. Bile produced by the liver. It is stored in the gall bladder and secreted into the duodenum via the bile duct (see diagram 11.14). (Note that the horse, deer, parrot and rat have no gall bladder). Bile is not a digestive enzyme.

Its function is to break up large globules of fat into smaller ones so the fat splitting enzymes can gain access the fat molecules. Diagram 11.14 - The liver, gall bladder and pancreas Pancreatic juice[ edit ] The pancreas is a gland located near the beginning of the duodenum (see diagram 11.14). In most animals it is large and easily seen but in rodents and rabbits it lies within the membrane linking the loops of the intestine (the mesentery) and is quite difficult to find. Pancreatic juice is produced in the pancreas. It flows into the duodenum and contains amylase for digesting starch, lipase for digesting fats and protease for digesting proteins. Intestinal juice[ edit ] Intestinal juice is produced by glands in the lining of the small intestine. It contains enzymes for digesting disaccharides and proteins as well as mucus and salts to make the contents of the small intestine more alkaline so the enzymes can work. Absorption[ edit ] The small molecules produced by digestion are absorbed into the villi of the wall of the small intestine. The tiny finger-like projections of the villi increase the surface area for absorption.

Glucose and amino acids pass directly through the wall into the blood stream by diffusion or active transport. Fatty acids and glycerol enter vessels of the lymphatic system (lacteals) that run up the centre of each villus. The Liver[ edit ] The liver is situated in the abdominal cavity adjacent to the diaphragm (see diagrams 2 and 14). It is the largest single organ of the body and has over 100 known functions. Its most important digestive functions are: the production of bile to help the digestion of fats (described above) and the control of blood sugar levels Glucose is absorbed into the capillaries of the villi of the intestine. The blood stream takes it directly to the liver via a blood vessel known as the hepatic portal vessel or vein (see diagram 11.15). The liver converts this glucose into glycogen which it stores. When glucose levels are low the liver can convert the glycogen back into glucose. It releases this back into the blood to keep the level of glucose constant. The hormone insulin, produced by special cells in the pancreas, controls this process.

Diagram 11.15 - The control of blood glucose by the liver Other functions of the liver include: 3. making vitamin A, 4. making the proteins that are found in the blood plasma (albumin, globulin and fibrinogen), 5. storing iron, 6. removing toxic substances like alcohol and poisons from the blood and converting them to safer substances, 7. producing heat to help maintain the temperature of the body. Diagram 11.16 - Summary of the main functions of the different regions of the gut Summary[ edit ] The gut breaks down plant and animal materials into nutrients that can be used by animals’ bodies. Plant material is more difficult to break down than animal tissue. The gut of herbivores is therefore longer and more complex than that of carnivores. Herbivores usually have a compartment (the rumen or functional caecum) housing micro-organisms to break down the cellulose wall of plants. Chewing by the teeth begins the food processing. There are 4 main types of teeth: incisors, canines, premolars and molars.

In dogs and cats the premolars and molars are adapted to slice against each other and are called carnassial teeth. Saliva is secreted in the mouth. It lubricates the food for swallowing and contains an enzyme to break down starch. Chewed food is swallowed and passes down the oesophagus by waves of contraction of the wall called peristalsis. The food passes to the stomach where it is churned and mixed with acidic gastric juice that begins the digestion of protein. The resulting chyme passes down the small intestine where enzymes that digest fats, proteins and carbohydrates are secreted. Bile produced by the liver is also secreted here. It helps in the breakdown of fats. Villi provide the large surface area necessary for the absorption of the products of digestion. In the colon and caecum water is absorbed and micro organisms produce some vitamin B and K. In rabbits, horses and rodents the caecum is enlarged as a functional caecum and micro-organisms break down cellulose cell walls to simpler carbohydrates. Waste products exit the body via the rectum and anus. The pancreas produces pancreatic juice that contains many of the enzymes secreted into the small intestine.

In addition to producing bile the liver regulates blood sugar levels by converting glucose absorbed by the villi into glycogen and storing it. The liver also removes toxic substances from the blood, stores iron, makes vitamin A and produces heat. Worksheet[ edit ] Use the Digestive System Worksheet to help you learn the different parts of the digestive system and their functions. Test Yourself[ edit ] Then work through the Test Yourself below to see if you have understood and remembered what you learned. 1. Name the four different kinds of teeth 2. Give 2 facts about how the teeth of cats and dogs are adapted for a carnivorous diet: 1. 3. What does saliva do to the food? 4. What is peristalsis? 5. What happens to the food in the stomach? 6. What is chyme? 7. Where does the chyme go after leaving the stomach? 8. What are villi and what do they do? 9. What happens in the small intestine? 10. Where is the pancreas and what does it do? 11. How does the caecum of rabbits differ from that of cats? 12. How does the liver help control the glucose levels in the blood? 13.

Give 2 other functions of the liver: 1. food chain - National Geographic Society food chain The heron and the fish are links in the food chain. Photograph by Ernie Aranyosi, MyShot Links in the Chain Organisms consume nutrients from a variety of different sources in the food chain. Xylophages eat wood. Termites and bark beetles are xylophages. Coprophages eat animal feces. Dung beetles and flies are coprophages. Geophages eat earth, such as clay or soil. Parrots and cockatoos are geophages. Palynivores eat pollen. Honeybees and some butterflies are palynivores. Lepidophages are fish that eat the scales (but not the body) of other fish. Some piranha and some catfish are lepidophages. Mucophages eat mucus. Usually, these tiny organisms live in the gills of fish. Carnivorous . . . Plants? Most plants on Earth take energy from the sun and nutrients from the soil. A few plants, however, get their nutrients from animals. These carnivorous plants include pitcher plants, Venus flytraps, and bladderworts.

These plants attract and trap preyusually insectsand then break them down with digestive enzymes. The food chain describes who eats whom in the wild. Every living thing—from one-celled algae to giant blue whale s—needs food to survive . Each food chain is a possible pathway that energy and nutrient s can follow through the ecosystem . For example, grass produces its own food from sunlight. A rabbit eats the grass. A fox eats the rabbit. When the fox dies, bacteria break down its body, returning it to the soil where it provides nutrients for plants like grass. Of course, many different animals eat grass, and rabbits can eat other plants besides grass. Foxes, in turn, can eat many types of animals and plants. Each of these living things can be a part of multiple food chains. All of the interconnected and overlapping food chains in an ecosystem make up a food web . Trophic Levels Organisms in food chains are grouped into categories called trophic level s. Roughly speaking, these levels are divided into producer s (first trophic level), consumer s (second, third, and fourth trophic levels), and decomposer s. Producers, also known as autotroph s, make their own food.

They make up the first level of every food chain. Autotrophs are usually plant s or one-celled organisms. Nearly all autotrophs use a process called photosynthesis to create “food” (a nutrient called glucose ) from sunlight, carbon dioxide , and water. Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed , are autotrophic. Phytoplankton , tiny organisms that live in the ocean, are also autotrophs. Some types of bacteria are autotrophs. For example, bacteria living in active volcano es use sulfur compounds to produce their own food. This process is called chemosynthesis . The second trophic level consists of organisms that eat the producers. These are called primary consumer s, or herbivore s. Deer, turtles, and many types of birds are herbivores. Secondary consumers eat the herbivores. Tertiary consumer s eat the secondary consumers. There may be more levels of consumers before a chain finally reaches its top predator. Top predator s, also called apex predator s, eat other consumers.

Consumers can be carnivore s (animals that eat other animals) or omnivore s (animals that eat both plants and animals). Omnivores, like people, consume many types of foods. People eat plants, such as vegetables and fruits. We also eat animals and animal products, such as meat, milk, and eggs. We eat fungi , such as mushrooms. We also eat algae, in edible seaweeds like nori (used to wrap sushi rolls) and sea lettuce (used in salads). Detritivore s and decomposers are the final part of food chains. Detritivores are organisms that eat nonliving plant and animal remains. For example, scavenger s such as vultures eat dead animals. Dung beetles eat animal feces . Decomposers like fungi and bacteria complete the food chain. They turn organic wastes, such as decay ing plants, into inorganic materials, such as nutrient-rich soil. Decomposers complete the cycle of life, returning nutrients to the soil or oceans for use by autotrophs. This starts a whole new food chain. Food Chains Different habitats and ecosystems provide many possible food chains that make up a food web.

In one marine food chain, single-celled organisms called phytoplankton provide food for tiny shrimp called krill . Krill provide the main food source for the blue whale, an animal on the third trophic level. In a grassland ecosystem, a grasshopper might eat grass, a producer. The grasshopper might get eaten by a rat, which in turn is consumed by a snake. Finally, a hawk—an apex predator—swoops down and snatches up the snake. In a pond, the autotroph might be algae. A mosquito larva eats the algae, and then perhaps a dragonfly larva eats the young mosquito. The dragonfly larva becomes food for a fish, which provides a tasty meal for a raccoon. Term (singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds. apex predator Noun species at the top of the food chain, with no predators of its own. Also called an alpha predator or top predator. autotroph Noun organism that can produce its own food and nutrients from chemicals in the atmosphere, usually through photosynthesis or chemosynthesis. (singular: bacterium) single-celled organisms found in every ecosystem on Earth.

blue whale species of marine mammal that is the largest animal to have ever lived. carbon dioxide Noun greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels. carnivore chemosynthesis Noun process by which some microbes turn carbon dioxide and water into carbohydrates using energy obtained from inorganic chemical reactions. consumer Noun organism on the food chain that depends on autotrophs (producers) or other consumers for food, nutrition, and energy. decay organism that breaks down dead organic material. detritivore organism that consumes dead plant material. ecosystem able to be eaten and digested. energy waste material produced by the living body of an organism. food chain Noun group of organisms linked in order of the food they eat, from producers to consumers, and from prey, predators, scavengers, and decomposers. fungi Plural Noun (singular: fungus) organisms that survive by decomposing and absorbing nutrients in organic material such as soil or dead organisms. glucose "simple sugar" chemical produced by many plants during photosynthesis. grassland ecosystem with large, flat areas of grasses.

herbivore small marine crustacean, similar to shrimp. larva a new or immature insect or other type of invertebrate. multiple red algae that is often dried and used to wrap sushi. nutrient photosynthesis Noun process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars. phytoplankton Noun microscopic organism that lives in the ocean and can convert light energy to chemical energy through photosynthesis. plant organism that produces its own food through photosynthesis and whose cells have walls. primary consumer organism that eats plants or other autotrophs. producer Noun organism on the food chain that can produce its own energy and nutrients. Also called an autotroph. scavenger seaweed with large, flat leaves. seaweed Noun marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria. secondary consumer chemical element with the symbol S. survive bite-sized rolls or balls of sticky rice topped with seafood or vegetables. tertiary consumer carnivore that mostly eats other carnivores. top predator Noun species at the top of the food chain, with no predators of its own.

Also called an alpha predator or apex predator. trophic level Noun one of three positions on the food chain: autotrophs (first), herbivores (second), and carnivores and omnivores (third). volcano Noun an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions. Lesson 4: Food Chains | MpalaLive Lesson 4: Food Chains U.S. Teaching Standards Objectives Students will learn about food chains, pyramids, and food webs. Students will also learn how all of nature is connected and dependent on each other. Background A food chain shows how each living thing gets its food. Some animals eat plants and some animals eat other animals. For example, a simple food chain links the trees and shrubs, the giraffes (that eat trees and shrubs), and the lions (that eat the giraffes). Each link in this chain is food for the next link. All food chains start with energy from the sun. This energy is captured by plants. Thus the living part of a food chain always starts with plant life and ends with an animal.

Plants are called producers because they are able to use light energy from the sun to produce food (sugar) from carbon dioxide and water. Animals cannot make their own food so they must eat plants and/or other animals. They are called consumers. There are three groups of consumers. Animals that eat only plants are called herbivores (or primary consumers). Animals that eat other animals are called carnivores. Carnivores that eat herbivores are called secondary consumers, and carnivores that eat other carnivores are called tertiary consumers. Animals and people who eat both animals and plants are called omnivores. Then there are decomposers (bacteria, fungi, and even some worms), which feed on decaying matter. These decomposers speed up the decaying process that releases mineral salts back into the food chain for absorption by plants as nutrients. In a food chain, energy is passed from one link to another. When a herbivore eats, only a fraction of the energy (that it gets from the plant food) becomes new body mass; the rest of the energy is lost as waste or used up by the herbivore to carry out its life processes (e.g., movement, digestion, reproduction).

Therefore, when the herbivore is eaten by a carnivore, it passes only a small amount of total energy (that it has received) to the carnivore. Of the energy transferred from the herbivore to the carnivore, some energy will be “wasted” or “used up” by the carnivore. The carnivore then has to eat many herbivores to get enough energy to grow. Because of the large amount of energy that is lost at each link, the amount of energy that is transferred decreases each time. The further along the food chain you go, the less food (and hence energy) remains available. Food chains can also be represented in different forms such as this pyramid. The above energy pyramid shows many trees and shrubs providing food and energy to giraffes. Note that as we go up, there are fewer giraffes than trees and shrubs and even fewer lions than giraffes. As we go further along a food chain, there are fewer and fewer consumers. In other words, a large mass of living things at the base is required to support a few at the top. Many herbivores are needed to support a few carnivores. Most food chains have no more than four or five links.

There cannot be too many links in a single food chain because the animals at the end of the chain would not get enough food (and hence, energy) to stay alive. Most animals are part of more than one food chain and eat more than one kind of food in order to meet their food and energy requirements. These interconnected food chains form a food web. Food chains can get complicated because animals usually eat a variety of food. Materials Food Chains Enough strips of colored paper so that each student has four, one on which to draw the sun, one on which to draw a producer, one on which to draw a primary consumer and one on which to draw a secondary consumer.

Food Web Carnivore: an organism that eats mostly meat Consumer: an organism, usually an animal, that feeds on plants or other animals Food chain: a sequence of organisms arranged in such a way that each feeds on the organism below it in the chain and serves as a source of food for the organism above Food web: all the connected or linked food chains within an ecological community Herbivore: an organism that eats mostly plants Predator: an animal that lives by killing and eating other animals Producer: an organism, usually a plant, that converts sunlight energy into living material; usually the first step on the food chain or food web or first trophic level of a food pyramid Preparation Cut enough strips of paper so that each student will have four. Cut the yarn into pieces that will connect species that interact with each other. Procedure Food Chains On the blackboard, write the following headings: Producers, Primary Consumers, Secondary Consumers, and Tertiary Consumers. Ask students to name some species under each heading. Then demonstrate how to create a food chain, using some of the species listed. Once students understand, have them draw the sun, a producer, a primary consumer, a secondary consumer, and a tertiary consumer on each of their four strips.

These should then be interlocked and glued together to make a chain of species in which one eats the other. They can be hung from the rafters to illustrate the diversity of food chains that exist in nature. Food Webs Note: This activity can be added for older students. Start as with food chains, putting the three headings on the board. Have students name species under each heading and tell something about each species’ lifestyle. Then have each student choose a species from the board, write its name on a card, and draw a picture of it. (Check each one off the list as it’s chosen, to make sure it’s only used once). Then the student should poke a hole near the bottom of the card. Begin the food web by attaching a picture of the sun at one side of the wall. (If you put it on a wall, it can be saved). Have the students who drew producers bring their cards up. Hang these in a horizontal line next to the sun and attach each one to the sun with a piece of yarn to show the connection. Then have students who drew primary consumers bring their cards up. Hang these in a horizontal line above the producers. One at a time, discuss which producers they would each consume.

Attach yarn from each primary consumer to the producers it would consume. (Remember that most animals eat more than one kind of food). The students will begin to see how complex a food web is. Next add the secondary and tertiary consumers in rows above the producers. Again, discuss the connections between primary, secondary, and tertiary consumers. Next add the scavengers: hyenas (can be predators as well as scavengers) and vultures . Finally, discuss decomposers—bacteria, fungi and worms that feed on the decaying matter—and their role in the food web. Students should now have a complete understanding of the complexity of the food web. At right is an example of a food web. Discussion All living things need energy to stay alive. This energy comes from the sun. Plants make their food from energy from the sun. Animals get their energy from the food they eat. Animals depend on other living things for food. Some animals eat plants while others eat other animals. This passing of energy from the sun to plants to animals to other animals is called a food chain. Possible Questions Do you know why there are more herbivores than carnivores? What if one animal from the food chain disappeared?

What about one level of the food chain? Producers? Decomposers ? Herbivores? How do humans fit in the food chain? What could happen if an animal not native to an area is brought into the local food chain? What could happen if you remove an animal from the food chain? How can sun and rain affect the food chain? Drought? Why is a food web a more accurate depiction of nature than a food chain or pyramid? Extension 1. Web of Life Objective: Students will understand the concept of a food chain and demonstrate a grassland’s food chain. Materials: Pictures of animals, river, tree, grass, sun A ball of yarn/spool of twine Procedure: Read The Great Kapok Tree, by Lynne Cherry. Ask students to name all the different animals that are dependent on the one tree. Give each participant a picture. First demonstrate a food chain, a simple interdependence , by linking the student with the sun card (the source of all energy) to the student with the grass card to the student with the zebra card to the student with the lion card. Show the impacts of man on the simple food chain.

Man can: Cut trees (no trees, nothing for grazers to eat, grazers will die, lions and other predators will have nothing to eat. They will start to eat our livestock.) Hunt in excess (If we kill the lions, there will be too many zebras and they will need more grass. They will eat the grass from our pasturelands.) Balance is key! Explain that the interactions in a grasslands system are more complicated than this. For example, the sun provides for more than just grass, and lions don’t only eat zebras. Have the participants now stand in a circle, out of order (i.e. not all of the producers together, then the primary consumers, then the secondary consumers, etc.) Give the ball of string to the person with the sun. Then ask that person to pass the yarn to the person with a card of an organism that the sun supports. If the sun supports more than one organism in the circle, pass the string back to the sun and from the sun to the other organism that it supports. Continue by asking the plants which organisms they can support and so on. Keep going through the chain until you get to the top consumers. The string will be a tangled web in the middle of the circle.

Food chains are complicated, and the balance they create is essential. Again discuss the impacts of man on the web by having students drop their string if man’s impact kills off their organism. For example, the impact of overhunting will cause the lions to drop their strings. What happens? Possible Questions Do you know why there are more herbivores than carnivores? What if one animal from the food chain disappeared? What about one level of the food chain? Producers? Decomposers? Herbivores? How do humans fit in the food chain? What could happen if an animal not native to an area is brought into the local food chain? What could happen if you remove an animal from the food chain? How can sun and rain affect the food chain? Drought? Why is a food web a more accurate depiction of nature than a food chain or pyramid? 2. Food Chain Tag This activity requires a large open area. In a class of 25 to 40 students, choose three to five to be predators and seven to ten to be plant-eaters. The remainder will be plants.

This represents a balanced system where plants are more plentiful than plant-eaters, plant-eaters more plentiful than predators, and predators are the least plentiful. The students can select which plant-eaters and predators will be in their groups. (Example: Grevy’s zebras are plant-eaters and lions are predators). Each group selects hand-signals that will differentiate them from the other groups. (Example: the plants may want to hold their hands out to their sides to represent leaves, the plant-eaters ( oryx ) may hold their hands on the heads to represent horns, and the predators (lions) may hold their hands up like paws with the claws showing). The predators try to tag the plant-eaters who try to tag the plants. Since predators decompose when they die and become fertilizer, the plants try to tag the predators. Once you are tagged, you turn into whatever tagged you. After a period of time, stop the game to see how many plants, plant-eaters, and predators are left. Play should resume but should be stopped a few times before the end to determine what has happened and why. After playing a few rounds of the game, select one of the plants to re-enter the game as a human.

The rules for the human are different: the human can tag anyone, but no one can tag the human. Each time the human tags someone, that player becomes another human. See how long it takes before all players have become changed into humans. Discuss the changes and relationships that the game illustrates. Some questions for discussion might include: What happens to the plants and plant-eaters if many of the predators have been caught? What happens to the plants if many of them have been caught? What happens when humans use too much of the food chain? How can we keep that from happening? Ask students to record what happened in their science notebooks, including an illustration of the food chain they represented. Talk about the adaptations the various organisms would have to develop in order to survive if one of the species in the food chain became extinct . The Comparative Anatomy of Eating - Vegsource.com The Comparative Anatomy of Eating Milton R. Mills, M.D. | 11/21/09 Email This Story to a Friend Your friend's email address: Your email address: Message (optional): Humans are most often described as "omnivores." This classification is based on the "observation" that humans generally eat a wide variety of plant and animal foods.

However, culture, custom and training are confounding variables when looking at human dietary practices. Thus, "observation" is not the best technique to use when trying to identify the most "natural" diet for humans. While most humans are clearly "behavioral" omnivores, the question still remains as to whether humans are anatomically suited for a diet that includes animal as well as plant foods. A better and more objective technique is to look at human anatomy and physiology. Mammals are anatomically and physiologically adapted to procure and consume particular kinds of diets. (It is common practice when examining fossils of extinct mammals to examine anatomical features to deduce the animal's probable diet.) Therefore, we can look at mammalian carnivores, herbivores (plant-eaters) and omnivores to see which anatomical and physiological features are associated with each kind of diet. Then we can look at human anatomy and physiology to see in which group we belong. Oral Cavity Carnivores have a wide mouth opening in relation to their head size. This confers obvious advantages in developing the forces used in seizing, killing and dismembering prey.

Facial musculature is reduced since these muscles would hinder a wide gape, and play no part in the animal's preparation of food for swallowing. In all mammalian carnivores, the jaw joint is a simple hinge joint lying in the same plane as the teeth. This type of joint is extremely stable and acts as the pivot point for the "lever arms" formed by the upper and lower jaws. The primary muscle used for operating the jaw in carnivores is the temporalis muscle. This muscle is so massive in carnivores that it accounts for most of the bulk of the sides of the head (when you pet a dog, you are petting its temporalis muscles). The "angle" of the mandible (lower jaw) in carnivores is small. This is because the muscles (masseter and pterygoids) that attach there are of minor importance in these animals. The lower jaw of carnivores cannot move forward, and has very limited side-to-side motion. When the jaw of a carnivore closes, the blade-shaped cheek molars slide past each other to give a slicing motion that is very effective for shearing meat off bone. The teeth of a carnivore are discretely spaced so as not to trap stringy debris.

The incisors are short, pointed and prong-like and are used for grasping and shredding. The canines are greatly elongated and dagger-like for stabbing, tearing and killing prey. The molars (carnassials) are flattened and triangular with jagged edges such that they function like serrated-edged blades. Because of the hinge-type joint, when a carnivore closes its jaw, the cheek teeth come together in a back-to-front fashion giving a smooth cutting motion like the blades on a pair of shears. The saliva of carnivorous animals does not contain digestive enzymes. When eating, a mammalian carnivore gorges itself rapidly and does not chew its food. Since proteolytic (protein-digesting) enzymes cannot be liberated in the mouth due to the danger of autodigestion (damaging the oral cavity), carnivores do not need to mix their food with saliva; they simply bite off huge chunks of meat and swallow them whole. According to evolutionary theory, the anatomical features consistent with an herbivorous diet represent a more recently derived condition than that of the carnivore.

Herbivorous mammals have well-developed facial musculature, fleshy lips, a relatively small opening into the oral cavity and a thickened, muscular tongue. The lips aid in the movement of food into the mouth and, along with the facial (cheek) musculature and tongue, assist in the chewing of food. In herbivores, the jaw joint has moved to position above the plane of the teeth. Although this type of joint is less stable than the hinge-type joint of the carnivore, it is much more mobile and allows the complex jaw motions needed when chewing plant foods. Additionally, this type of jaw joint allows the upper and lower cheek teeth to come together along the length of the jaw more or less at once when the mouth is closed in order to form grinding platforms. (This type of joint is so important to a plant-eating animal, that it is believed to have evolved at least 15 different times in various plant-eating mammalian species.) The angle of the mandible has expanded to provide a broad area of attachment for the well-developed masseter and pterygoid muscles (these are the major muscles of chewing in plant-eating animals). The temporalis muscle is small and of minor importance.

The masseter and pterygoid muscles hold the mandible in a sling-like arrangement and swing the jaw from side-to-side. Accordingly, the lower jaw of plant-eating mammals has a pronounced sideways motion when eating. This lateral movement is necessary for the grinding motion of chewing. The dentition of herbivores is quite varied depending on the kind of vegetation a particular species is adapted to eat. Although these animals differ in the types and numbers of teeth they posses, the various kinds of teeth when present, share common structural features. The incisors are broad, flattened and spade-like. Canines may be small as in horses, prominent as in hippos, pigs and some primates (these are thought to be used for defense) or absent altogether. The molars, in general, are squared and flattened on top to provide a grinding surface. The molars cannot vertically slide past one another in a shearing/slicing motion, but they do horizontally slide across one another to crush and grind. The surface features of the molars vary depending on the type of plant material the animal eats.

The teeth of herbivorous animals are closely grouped so that the incisors form an efficient cropping/biting mechanism, and the upper and lower molars form extended platforms for crushing and grinding. The "walled-in" oral cavity has a lot of potential space that is realized during eating. These animals carefully and methodically chew their food, pushing the food back and forth into the grinding teeth with the tongue and cheek muscles. This thorough process is necessary to mechanically disrupt plant cell walls in order to release the digestible intracellular contents and ensure thorough mixing of this material with their saliva. This is important because the saliva of plant-eating mammals often contains carbohydrate-digesting enzymes which begin breaking down food molecules while the food is still in the mouth. Stomach and Small Intestine Striking differences between carnivores and herbivores are seen in these organs. Carnivores have a capacious simple (single-chambered) stomach. The stomach volume of a carnivore represents 60-70% of the total capacity of the digestive system. Because meat is relatively easily digested, their small intestines (where absorption of food molecules takes place) are short&151;about three to five or six times the body length.

Since these animals average a kill only about once a week, a large stomach volume is advantageous because it allows the animals to quickly gorge themselves when eating, taking in as much meat as possible at one time which can then be digested later while resting. Additionally, the ability of the carnivore stomach to secrete hydrochloric acid is exceptional. Carnivores are able to keep their gastric pH down around 1-2 even with food present. This is necessary to facilitate protein breakdown and to kill the abundant dangerous bacteria often found in decaying flesh foods. Because of the relative difficulty with which various kinds of plant foods are broken down (due to large amounts of indigestible fibers), herbivores have significantly longer and in some cases, far more elaborate guts than carnivores. Herbivorous animals that consume plants containing a high proportion of cellulose must "ferment" (digest by bacterial enzyme action) their food to obtain the nutrient value. They are classified as either "ruminants" (foregut fermenters) or hindgut fermenters. The ruminants are the plant-eating animals with the celebrated multiple-chambered stomachs.

Herbivorous animals that eat a diet of relatively soft vegetation do not need a multiple-chambered stomach. They typically have a simple stomach, and a long small intestine. These animals ferment the difficult-to-digest fibrous portions of their diets in their hindguts (colons). Many of these herbivores increase the sophistication and efficiency of their GI tracts by including carbohydrate-digesting enzymes in their saliva. A multiple-stomach fermentation process in an animal which consumed a diet of soft, pulpy vegetation would be energetically wasteful. Nutrients and calories would be consumed by the fermenting bacteria and protozoa before reaching the small intestine for absorption. The small intestine of plant-eating animals tends to be very long (greater than 10 times body length) to allow adequate time and space for absorption of the nutrients. Colon The large intestine (colon) of carnivores is simple and very short, as its only purposes are to absorb salt and water. It is approximately the same diameter as the small intestine and, consequently, has a limited capacity to function as a reservoir. The colon is short and non-pouched. The muscle is distributed throughout the wall, giving the colon a smooth cylindrical appearance.

Although a bacterial population is present in the colon of carnivores, its activities are essentially putrefactive. In herbivorous animals, the large intestine tends to be a highly specialized organ involved in water and electrolyte absorption, vitamin production and absorption, and/or fermentation of fibrous plant materials. The colons of herbivores are usually wider than their small intestine and are relatively long. In some plant-eating mammals, the colon has a pouched appearance due to the arrangement of the muscle fibers in the intestinal wall. Additionally, in some herbivores the cecum (the first section of the colon) is quite large and serves as the primary or accessory fermentation site. What About Omnivores? One would expect an omnivore to show anatomical features which equip it to eat both animal and plant foods. According to evolutionary theory, carnivore gut structure is more primitive than herbivorous adaptations. Thus, an omnivore might be expected to be a carnivore which shows some gastrointestinal tract adaptations to an herbivorous diet. This is exactly the situation we find in the Bear, Raccoon and certain members of the Canine families.

(This discussion will be limited to bears because they are, in general, representative of the anatomical omnivores.) Bears are classified as carnivores but are classic anatomical omnivores. Although they eat some animal foods, bears are primarily herbivorous with 70-80% of their diet comprised of plant foods. (The one exception is the Polar bear which lives in the frozen, vegetation poor arctic and feeds primarily on seal blubber.) Bears cannot digest fibrous vegetation well, and therefore, are highly selective feeders. Their diet is dominated by primarily succulent lent herbage, tubers and berries. Many scientists believe the reason bears hibernate is because their chief food (succulent vegetation) not available in the cold northern winters. (Interestingly, Polar bears hibernate during the summer months when seals are unavailable.) In general, bears exhibit anatomical features consistent with a carnivorous diet. The jaw joint of bears is in the same plane as the molar teeth. The temporalis muscle is massive, and the angle of the mandible is small corresponding to the limited role the pterygoid and masseter muscles play in operating the jaw.

The small intestine is short (less than five times body length) like that of the pure carnivores, and the colon is simple, smooth and short. The most prominent adaptation to an herbivorous diet in bears (and other "anatomical" omnivores) is the modification of their dentition. Bears retain the peg-like incisors, large canines and shearing premolars of a carnivore; but the molars have become squared with rounded cusps for crushing and grinding. Bears have not, however, adopted the flattened, blunt nails seen in most herbivores and retain the elongated, pointed claws of a carnivore. An animal which captures, kills and eats prey must have the physical equipment which makes predation practical and efficient. Since bears include significant amounts of meat in their diet, they must retain the anatomical features that permit them to capture and kill prey animals. Hence, bears have a jaw structure, musculature and dentition which enable them to develop and apply the forces necessary to kill and dismember prey even though the majority of their diet is comprised of plant foods.

Although an herbivore-style jaw joint (above the plane of the teeth) is a far more efficient joint for crushing and grinding vegetation and would potentially allow bears to exploit a wider range of plant foods in their diet, it is a much weaker joint than the hinge-style carnivore joint. The herbivore-style jaw joint is relatively easily dislocated and would not hold up well under the stresses of subduing struggling prey and/or crushing bones (nor would it allow the wide gape carnivores need). In the wild, an animal with a dislocated jaw would either soon starve to death or be eaten by something else and would, therefore, be selected against. A given species cannot adopt the weaker but more mobile and efficient herbivore-style joint until it has committed to an essentially plant-food diet test it risk jaw dislocation, death and ultimately, extinction. What About Me? The human gastrointestinal tract features the anatomical modifications consistent with an herbivorous diet. Humans have muscular lips and a small opening into the oral cavity. Many of the so-called "muscles of expression" are actually the muscles used in chewing. The muscular and agile tongue essential for eating, has adapted to use in speech and other things.

The mandibular joint is flattened by a cartilaginous plate and is located well above the plane of the teeth. The temporalis muscle is reduced. The characteristic "square jaw" of adult males reflects the expanded angular process of the mandible and the enlarged masseter/pterygoid muscle group. The human mandible can move forward to engage the incisors, and side-to-side to crush and grind. Human teeth are also similar to those found in other herbivores with the exception of the canines (the canines of some of the apes are elongated and are thought to be used for display and/or defense). Our teeth are rather large and usually abut against one another. The incisors are flat and spade-like, useful for peeling, snipping and biting relatively soft materials. The canines are neither serrated nor conical, but are flattened, blunt and small and function Like incisors. The premolars and molars are squarish, flattened and nodular, and used for crushing, grinding and pulping noncoarse foods. Human saliva contains the carbohydrate-digesting enzyme, salivary amylase. This enzyme is responsible for the majority of starch digestion.

The esophagus is narrow and suited to small, soft balls of thoroughly chewed food. Eating quickly, attempting to swallow a large amount of food or swallowing fibrous and/or poorly chewed food (meat is the most frequent culprit) often results in choking in humans. Man's stomach is single-chambered, but only moderately acidic. (Clinically, a person presenting with a gastric pH less than 4-5 when there is food in the stomach is cause for concern.) The stomach volume represents about 21-27% of the total volume of the human GI tract. The stomach serves as a mixing and storage chamber, mixing and liquefying ingested foodstuffs and regulating their entry into the small intestine. The human small intestine is long, averaging from 10 to 11 times the body length. (Our small intestine averages 22 to 30 feet in length. Human body size is measured from the top of the head to end of the spine and averages between two to three feet in length in normal-sized individuals.) The human colon demonstrates the pouched structure peculiar to herbivores. The distensible large intestine is larger in cross-section than the small intestine, and is relatively long.

Man's colon is responsible for water and electrolyte absorption and vitamin production and absorption. There is also extensive bacterial fermentation of fibrous plant materials, with the production and absorption of significant amounts of food energy (volatile short-chain fatty acids) depending upon the fiber content of the diet. The extent to which the fermentation and absorption of metabolites takes place in the human colon has only recently begun to be investigated. In conclusion, we see that human beings have the gastrointestinal tract structure of a "committed" herbivore. Humankind does not show the mixed structural features one expects and finds in anatomical omnivores such as bears and raccoons. Thus, from comparing the gastrointestinal tract of humans to that of carnivores, herbivores and omnivores we must conclude that humankind's GI tract is designed for a purely plant-food diet. SUMMARY

Question: What name is given to animals that eat both flesh and plant material?
Answer: Omnivores